Planar microphotonic circuits

Abstract

A microphotonic circuit includes one or more light control elements such as modulators or switches coupled in polymer waveguides, and controlled by electrical bias fields produced by voltage or light sources. Each modulator or switch includes at least one polymer waveguide having a high-η core and surrounding low-η cladding, to constrain the light. An electrooptic control element is evanescently coupled to the core of the first waveguide by spacing from the core. The coupling between the core and the control element depends upon the relative ηs of the core, cladding and electrooptic element. Bias is applied to maintain the electrooptic element in one of at least two possible states, one of which prevents coupling between the electrooptic element and the core, and the other of which permits such coupling. The bias may be applied in the form of electrical voltage or light. In some embodiments of the invention, a second optical waveguide is coupled to the electrooptic element. The coupling of the second waveguide may be evanescent or direct.

What is claimed is: 
     
       1. An optical assembly, comprising, a planar optical polymer first waveguide for guiding light having a selected linear polarization, and lying within a range of wavelengths, said first waveguide including an optical core having an index of refraction lying within a first range;   at least one planar control element evanescently coupled to said core of said first waveguide, for, in a first state, exhibiting an index of refraction which lies in a range which is less than said range of index of refraction of said core, and for, in a second state, exhibiting an index of refraction which lies in a range which is equal to or higher than said index of refraction of said core, said control element being made from a material which has an index of refraction which is responsive to the amplitude of electric fields traversing said control element;   a planar optical polymer second waveguide coupled to said control element for leading out that portion of an optical signal which passes from said first optical waveguide into said control element; and   means for coupling an electric field to said control element, for producing, within said control element, an electric field parallel with said selected linear polarization, and of a magnitude selected to place said control element in at least one of said first and second states, whereby in said first state of said material of said control element, optical signal in said first waveguide remains largely in said first waveguide, and in said second state of said material of said control element, at least some of said optical signal flowing in said first waveguide is coupled to said second waveguide.   
     
     
       2. An assembly according to claim 1, wherein said second waveguide is evanescently coupled to said control element. 
     
     
       3. An assembly according to claim 2, wherein said means for coupling an electric field comprises; first and second transparent, electrically conducting electrodes in electrical contact with different portions of said control element; and   coupling means coupled to said first and second transparent, electrically conducting electrodes, and adapted to be coupled to a source of bias voltage, for applying said bias voltage across said first and second electrodes, whereby a bias electric field extends between said first and second electrodes.   
     
     
       4. An assembly according to claim 3, wherein said transparent, electrically conducting electrodes are indium tin oxide. 
     
     
       5. An assembly according to claim 2, wherein said means for coupling an electric field comprises: a direct coupling of said second waveguide means to said control element; and   means adapted for coupling said second waveguide means to a source of bias light, for coupling said bias light to said control element, for thereby establishing said electric field.   
     
     
       6. An assembly according to claim 5, wherein said second waveguide means further comprises a waveguide portion which is substantially free of electrooptic effects; and a waveguide transition for coupling said waveguide portion of said second waveguide means to said control element in a manner which tends to reduce reflections of light from said control element toward said source of bias light.   
     
     
       7. An assembly according to claim 1, wherein said first and second waveguides are polarization-maintaining waveguides. 
     
     
       8. An assembly according to claim 1, wherein: said coupling means comprises opaque electrically conducting means.   
     
     
       9. An assembly according to claim 8, wherein said opaque electrically conducting means comprises gold. 
     
     
       10. An assembly according to claim 1, further comprising: a source of bias light; and   third waveguide means coupled to said source of bias light and directly coupled to said control element, for coupling said bias light to said control element, for thereby establishing said electric field.   
     
     
       11. An assembly according to claim 10, wherein said third waveguide means further comprises a waveguide portion which is substantially free of electrooptic effects; and a waveguide transition for coupling said third waveguide portion of said waveguide means to said control element in a manner which tends to reduce reflections of light from said control element toward said source of bias light.   
     
     
       12. An optical microchip, comprising, a first active device, said first active device including: (a) a planar optical polymer first waveguide for guiding light having a selected linear polarization, and lying within a range of wavelengths, said first waveguide including a first port, a second port, and an optical core extending between said first and second ports, said optical core having an index of refraction lying within a first range;   (b) at least one planar control element evanescently coupled to said core of said first waveguide, for, in a first state, exhibiting an index of refraction which lies in a range which is less than said range of index of refraction of said core, and for, in a second state, exhibiting an index of refraction which lies in a range which is equal to or higher than said index of refraction of said core, said control element being made from a material which has an index of refraction which is responsive to the amplitude of electric fields traversing said control element;   (c) electric field coupling means coupled to said control element and adapted for being coupled to a source of bias in the form of an electric field, for generating, within said control element, an electric field parallel with said selected linear polarization, and of a magnitude selected to place said control element in at least one of said first and second states, whereby in said first state of said material of said control element, optical signal in said first waveguide remains largely in said first waveguide, and in said second state of said material of said control element, a significant amount of said optical signal is lost while flowing between said first and second ports of said first waveguide;     and a second active device, said second active device comprising: (a) a planar optical polymer second waveguide for guiding light having said selected linear polarization, and lying within said range of wavelengths, said second waveguide including first and second ports, and an optical core extending between said first and second ports of said second waveguide, said optical core of said second active device having an index of refraction lying within a third range;   (b) at least a second planar control element evanescently coupled to said core of said second waveguide, for, in a first state, exhibiting an index of refraction which lies in a range which is less than said third range of index of refraction, and for, in a second state, exhibiting an index of refraction which lies in a range which is equal to or higher than said third range of index of refraction, said control element being made from a material which has an index of refraction which is responsive to the amplitude of electric fields traversing said control element; and   a planar, polarization-maintaining polymeric third waveguide extending on said microchip from said second port of said first waveguide to one of (i) said first port of said second waveguide and (ii) said second planar control element, for processing light in the cascade of said first and second active devices.     
     
     
       13. A microchip according to claim 12, further comprising: a planar optical polymer third waveguide coupled to said control element of said first active device, for leading out that portion of an optical signal which passes from said first optical waveguide into said control element of said first active device.   
     
     
       14. A microchip according to claim 12, wherein said one of said first port of said second waveguide and said second planar control element is said first port of said second waveguide. 
     
     
       15. A microchip according to claim 12, wherein said one of said first port of said second waveguide and said second planar control element is said second planar control element of said second waveguide.